Somatic cell genetic studies will utilize suspension cultures of plant cells. We shall select and purify different mutants. These will be used to construct a genetic map of soybean and Datura. Linkage groups will be defined using a fusion-segregation cycle and a cis-trans test. Complementation and three-factor crossovers will map within linkage groups. Ribosomal RNA genes exist as two classes in soybean, which differ with respect to the size of the spacer regions as determined by restriction mapping. One of the classes is lost following prolonged selection by slow growth of cells in nutritionally sub-optimal medium. R-loop mapping of the two classes is planned. We will clone the sequences and determine the nucleotide sequence of the spacer regions. The rate of loss and of reamplification of sequences will be measured. Other repeated sequences will be isolated and the loss and reamplification of this DNA and/or DNA will be measured between somatic hybrids and diploid or haploid cell lines. The time of synthesis in S of these sequences will be determined. 60% of the DNA of the Kangaroo rat, D. ordii, is a density rich satellite. In wild populations different proportions of high and low density DNA are found. We shall amplify the genes for methotrexate resistance and for PALA resistance and determine whether extra copies of these genes are found in satellite or main band DNA. Satellite DNAs from different populations of wild type cells will be examined for common and different repetitive and middle repetitive sequences.